Hydrogen bonding in the gas phase. Part 1.—Infra-red spectroscopic investigation of amine–alcohol systems

Abstract

An infra-red investigation has been made of gas-phase hydrogen bonding between a range of amines and alcohols. Frequency displacements of the O—H stretching vibration have been obtained for some thirty gas-phase hydrogen bonded complexes. These displacements for a series of amines provide a measure of the relative electron donating abilities of the free amines: Et₃N > Et₂NH ≈ Me₃N > Me₂NH > EtNH₂ > MeNH₂ > NH₃. Band contours for the O—H stretching mode of such gas-phase complexes are reported and discussed. These can be interpreted in terms of sum-and-difference bands of the O—H stretching vibration and the hydrogen bond stretching vibration. The interpretation can account for the qualitative changes in band contour that occur along a series of complexes. The systems considered include those formed by ammonia, methylamine, dimethylamine, trimethylamine, ethylamine and diethylamine with methanol, ethanol, isopropanol, t-butanol, and trifluoroethanol. Some complexes of triethylamine are also included.